Synchronization of transmission intervals in Wi-Fi

ABSTRACT

An access point generates a data packet such that the data packet has a same packet length as a data packet from at least one other access point. The access point reserves a channel for a time interval, and initiates transmission of the data packet over the channel at a same time as transmission of the data packet from the at least one other access point. As a result, the access point synchronizes its transmission interval with a transmission interval of the at least one other access point which reduces inter-access point interference.

BACKGROUND

Current Wi-Fi systems have unaligned time division duplexed (TDD)transmissions where one access point's (AP) downlink transmission mayinterfere with another access point's uplink transmission. This inter-APinterference is particularly a problem in high density networks wherewireless channels between APs are stronger than wireless channelsbetween APs and terminals. If the APs are not aligned in terms of thedownlink and uplink transmission intervals, then transmission by one ormore APs will strongly interfere and possibly block reception at otherlistening APs. This causes poor area capacity (bps/km²), packet loss,and over all lower data rates.

FIG. 1 illustrates an example problem of unaligned transmissions fromTDD Wi-Fi access points. FIG. 1 depicts a street canyon, where there isa direct Line of Sight (LOS) between the AP1 and AP2, andnon-line-of-sight (NLOS) between the APs and terminals (user equipmentUE1 and UE2). Thus, the coverage of AP2 is smaller than the interferencerange from AP1. If AP1 is transmitting a downlink signal DL at highpower to UE1, AP2 will find it hard to hear a weak uplink signal UL fromUE2.

SUMMARY

At least one example embodiment relates to an access point configured tosynchronize its transmission interval with a transmission interval of atleast one other access point in a communications network and/or a methodof synchronizing a transmission interval of an access point with atransmission interval of at least one other access point in acommunications network, which may reduce inter-access pointinterference.

According to at least one example embodiment, an access point isconfigured to generate a data packet such that the data packet has asame packet length as a data packet from at least one other accesspoint. The access point is configured to reserve a channel for a timeinterval, and to initiate transmission of the data packet over thechannel at a same time as transmission of the data packet from the atleast one other access point.

According to at least one example embodiment, the access point isconfigured to set a look-ahead window for the channel if there is thirdparty traffic on the channel, the look-ahead window containing a timewhen the channel is available for transmitting the data packet, and thelook-ahead window being based on the third party traffic.

According to at least one example embodiment, the access point isconfigured to exclude the third party traffic on the channel during thereserved time interval.

According to at least one example embodiment, the access point isconfigured to refuse uplink transmission requests for the channel from auser terminal associated with the access point during the reserved timeinterval.

According to at least one example embodiment, an access point isconfigured to first seize a channel to hold the channel. The accesspoint is configured to second seize the channel to initiate datatransmission over the channel, the data transmission for the accesspoint being initiated at a same time as initiation of data transmissionfor at least one other access point over the channel.

According to at least one example embodiment, the access point isconfigured to hold the channel by refusing uplink transmission requestsfor the channel from a user terminal associated with the access point.

According to at least one example embodiment, the access point isconfigured to set a look-ahead window if there is third party traffic onthe channel, the look-ahead window containing a time when a channel isavailable for data transmission to or from the access point, and theaccess point is configured to exclude a third party access point fromtransmitting over the channel during the look-ahead window and the datatransmission.

According to at least one example embodiment, a method of synchronizingdata transmission includes generating a plurality of data packets, eachdata packet being associated with a different access point in aplurality of access points; reserving a channel for a time interval; andsimultaneously initiating transmission of the plurality of data packetsover the channel during the reserved time interval.

According to at least one example embodiment, the generating includesinserting dummy data into at least one data packet such that each datapacket in the plurality of data packets has a same packet length.

According to at least one example embodiment, the simultaneouslyinitiating transmission includes removing random back-off for theplurality of access points.

According to at least one example embodiment, the reserving includesbroadcasting a reserve signal to refuse uplink transmission requestsfrom user terminals associated with the plurality of access pointsduring the reserved time interval.

According to at least one example embodiment, the reserving includessetting a look-ahead window for the channel if there is third partytraffic on the channel, the look-ahead window containing a time when thechannel is available for transmitting the plurality of data packets, andthe look-ahead window being based on the third party traffic.

According to at least one example embodiment, the reserving includesbroadcasting a reserve signal during the look-ahead window by theplurality of access points.

According to at least one example embodiment, the broadcasting thereserve signal holds the channel until the plurality of access pointssimultaneously initiate transmission of the plurality of data packets.

According to at least one example embodiment, the reserving includespreventing third party access point transmissions over the channelduring the reserved time interval.

According to at least one example embodiment, a method of reserving achannel includes first seizing, by a plurality of access points, to holdthe channel; and second seizing, by the plurality of access points, thechannel to simultaneously initiate data transmission to or from theplurality of access points.

According to at least one example embodiment, the first seizing includesrefusing uplink transmission requests for the channel from userterminals associated with the plurality of access points.

According to at least one example embodiment, the method furtherincludes setting a look-ahead window in the plurality of access pointsif there is third party traffic on the channel, the look-ahead windowcontaining a time when the channel is available for transmitting datapackets to or from the plurality of access points, the look-ahead windowbeing based on third party traffic.

According to at least one example embodiment, the first seizing includespreventing a third party access point from transmitting over the channelduring the look-ahead window and the data transmission.

According to at least one example embodiment, the method furtherincludes generating data packets for each of the plurality of accesspoints such that each data packet has a same packet length.

BRIEF DESCRIPTION OF THE DRAWINGS

Example embodiments will become more fully understood from the detaileddescription given herein below and the accompanying drawings, whereinlike elements are represented by like reference numerals, which aregiven by way of illustration only and thus are not limiting of exampleembodiments.

FIG. 1 illustrates unaligned time division duplexed (TDD) Wi-Fitransmissions resulting in inter-access point interference.

FIG. 2 is a diagram illustrating an example structure of an access pointin a communications network according to at least one exampleembodiment.

FIG. 3 illustrates a timeline of a protocol for aligning TDDtransmissions in a Wi-Fi network according to at least one exampleembodiment.

FIG. 4 is a flow diagram of a method for aligning transmissions in aWi-Fi network according to an example embodiment.

FIG. 5 is a flow diagram of a method for reserving a channel in a Wi-Finetwork according to an example embodiment.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

Various example embodiments will now be described more fully withreference to the accompanying drawings in which some example embodimentsare shown.

Detailed illustrative embodiments are disclosed herein. However,specific structural and functional details disclosed herein are merelyrepresentative for purposes of describing example embodiments. Thisinvention may, however, be embodied in many alternate forms and shouldnot be construed as limited to only the embodiments set forth herein.

Accordingly, while example embodiments are capable of variousmodifications and alternative forms, the embodiments are shown by way ofexample in the drawings and will be described herein in detail. Itshould be understood, however, that there is no intent to limit exampleembodiments to the particular forms disclosed. On the contrary, exampleembodiments are to cover all modifications, equivalents, andalternatives falling within the scope of this disclosure. Like numbersrefer to like elements throughout the description of the figures.

Although the terms first, second, etc. may be used herein to describevarious elements, these elements should not be limited by these terms.These terms are only used to distinguish one element from another. Forexample, a first element could be termed a second element, andsimilarly, a second element could be termed a first element, withoutdeparting from the scope of this disclosure. As used herein, the term“and/or,” includes any and all combinations of one or more of theassociated listed items.

When an element is referred to as being “connected,” or “coupled,” toanother element, it can be directly connected or coupled to the otherelement or intervening elements may be present. By contrast, when anelement is referred to as being “directly connected,” or “directlycoupled,” to another element, there are no intervening elements present.Other words used to describe the relationship between elements should beinterpreted in a like fashion (e.g., “between,” versus “directlybetween,” “adjacent,” versus “directly adjacent,” etc.).

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting. As used herein, thesingular forms “a,” “an,” and “the,” are intended to include the pluralforms as well, unless the context clearly indicates otherwise. It willbe further understood that the terms “comprises,” “comprising,”“includes,” and/or “including,” when used herein, specify the presenceof stated features, integers, steps, operations, elements, and/orcomponents, but do not preclude the presence or addition of one or moreother features, integers, steps, operations, elements, components,and/or groups thereof.

It should also be noted that in some alternative implementations, thefunctions/acts noted may occur out of the order noted in the figures.For example, two figures shown in succession may in fact be executedsubstantially concurrently or may sometimes be executed in the reverseorder, depending upon the functionality/acts involved.

Specific details are provided in the following description to provide athorough understanding of example embodiments. However, it will beunderstood by one of ordinary skill in the art that example embodimentsmay be practiced without these specific details. For example, systemsmay be shown in block diagrams so as not to obscure the exampleembodiments in unnecessary detail. In other instances, well-knownprocesses, structures and techniques may be shown without unnecessarydetail in order to avoid obscuring example embodiments.

In the following description, illustrative embodiments will be describedwith reference to acts and symbolic representations of operations (e.g.,in the form of flow charts, flow diagrams, data flow diagrams, structurediagrams, block diagrams, etc.) that may be implemented as programmodules or functional processes include routines, programs, objects,components, data structures, etc., that perform particular tasks orimplement particular abstract data types and may be implemented usingexisting hardware at existing network elements (e.g., base stations,base station controllers, NodeBs, eNodeBs, etc.). Such existing hardwaremay include one or more Central Processing Units (CPUs), digital signalprocessors (DSPs), application-specific-integrated-circuits, fieldprogrammable gate arrays (FPGAs) computers or the like.

Although a flow chart may describe the operations as a sequentialprocess, many of the operations may be performed in parallel,concurrently or simultaneously. In addition, the order of the operationsmay be re-arranged. A process may be terminated when its operations arecompleted, but may also have additional steps not included in thefigure. A process may correspond to a method, function, procedure,subroutine, subprogram, etc. When a process corresponds to a function,its termination may correspond to a return of the function to thecalling function or the main function.

As disclosed herein, the term “storage medium” or “computer readablestorage medium” may represent one or more devices for storing data,including read only memory (ROM), random access memory (RAM), magneticRAM, core memory, magnetic disk storage mediums, optical storagemediums, flash memory devices and/or other tangible machine readablemediums for storing information. The term “computer-readable medium” mayinclude, but is not limited to, portable or fixed storage devices,optical storage devices, and various other mediums capable of storing,containing or carrying instruction(s) and/or data.

Furthermore, example embodiments may be implemented by hardware,software, firmware, middleware, microcode, hardware descriptionlanguages, or any combination thereof. When implemented in software,firmware, middleware or microcode, the program code or code segments toperform the necessary tasks may be stored in a machine or computerreadable medium such as a computer readable storage medium. Whenimplemented in software, a processor or processors will perform thenecessary tasks.

A code segment may represent a procedure, function, subprogram, program,routine, subroutine, module, software package, class, or any combinationof instructions, data structures or program statements. A code segmentmay be coupled to another code segment or a hardware circuit by passingand/or receiving information, data, arguments, parameters or memorycontents. Information, arguments, parameters, data, etc. may be passed,forwarded, or transmitted via any suitable means including memorysharing, message passing, token passing, network transmission, etc.

FIG. 2 is a diagram illustrating an example structure of an access pointaccording to an example embodiment. According to at least one exampleembodiment, an access point (AP) 151 may be configured for use in acommunications network (e.g., a Wi-Fi network). Referring to FIG. 2, theaccess point 151 may include, for example, a data bus 159, atransmitting unit 152, a receiving unit 154, a memory unit 156, and aprocessing unit 158.

The transmitting unit 152, receiving unit 154, memory unit 156, andprocessing unit 158 may send data to and/or receive data from oneanother using the data bus 159. The transmitting unit 152 is a devicethat includes hardware and any necessary software for transmittingwireless signals including, for example, data signals, control signals,and signal strength/quality information via one or more wirelessconnections to other network elements in a communications network.

The receiving unit 154 is a device that includes hardware and anynecessary software for receiving wireless signals including, forexample, data signals, control signals, and signal strength/qualityinformation via one or more wireless connections to other networkelements in a communications network.

The memory unit 156 may be any device capable of storing data includingmagnetic storage, flash storage, etc.

The processing unit 158 may be any device capable of processing dataincluding, for example, a microprocessor configured to carry outspecific operations based on input data, or capable of executinginstructions included in computer readable code. For example, it shouldbe understood that the modifications and methods described below, withreference to FIGS. 3, 4 and 5, may be stored on the memory unit 156 andimplemented by the processing unit 158 within AP 151 from FIG. 2.

FIG. 3 illustrates a timeline of a protocol for aligning time divisionduplexed (TDD) Wi-Fi transmissions according to at least one exampleembodiment. As such, the discussion of example embodiments includes someterms, techniques, and structures considered to be well-known within theIEEE 802.11 standards (i.e., 802.11a, 802.11b, 802.11g, etc.).Accordingly, detailed discussions of well-known terms, techniques, andstructures have been omitted from this description. It should also beunderstood that this description should make apparent to one of ordinaryskill in the art how to implement the below described modifications,methods, and devices into existing protocol and existing systems.

According to FIG. 3, multiple access points (APs) in a Wi-Fi networkhave an identical downlink transmission interval (DTI). In other words,multiple APs simultaneously initiate data transmission over a channel ata beginning of the DTI, and simultaneously conclude the DTI withacknowledgements ACK. Each participating AP has a network wide time, viaGPS or network protocol by which downlink transmission intervals aredefined.

According to at least one example embodiment, coordination of APswishing to take part in the aligned transmission may occur through acentral server. For example, APs wishing to participate in transmissionalignment may register their individual MAC addresses with a centralserver that is broadcasting a time for the aligned transmission.Alternatively, APs may coordinate the aligned transmission via aself-organizing system, where some APs are broadcasting a time for thealigned transmission to allow other listening APs to join the alignedtransmission. Access points participating in the transmission alignmentmay be referred to as APs or participating APs. APs not participating inthe DTI alignment may be referred to as third party APs or third partytransmissions.

According to at least one example embodiment, there are some keymodifications to the media access control (MAC) layer which allowparticipating APs to align their transmissions. First, MAC protocol ismodified so that each participating AP creates identical packet startand finish times. A second modification to the AP MAC layer includesrefusing uplink transmissions that would overlap the downlinktransmission interval (DTI), thereby preventing the DTI from beingutilized by each of the APs' associated terminals. A third modificationto the AP MAC layer includes reserving the DTI, thereby preventing theDTI from being utilized by third party APs.

The above modifications to the MAC protocol as executed by eachparticipating AP are discussed below with reference to FIGS. 3, 4 and 5.It should be understood that these modifications and below describedmethods may be stored on a memory unit 156 and implemented by aprocessing unit 158 within a network element 151 from FIG. 2.

FIG. 4 illustrates a flow diagram of a method for aligning transmissionsin a Wi-Fi network according to at least one example embodiment.

In step S400 of FIG. 4, participating APs generate a plurality of datapackets such that each data packet has a same packet length. Referringto FIGS. 3 and 4, this may be accomplished by each AP creating identicalover-the-air packet lengths for physical layer protocol data units(PPDU) by inserting dummy data or dummy packet(s), where desired, intoan aggregated MAC service data unit (A-MSDU). As a result, the packetsfor each participating AP may have a same number of orthogonalfrequency-division multiplexing (OFDM) symbols (i.e., a same packetlength).

In step S410 of FIG. 4, each participating AP reserves a channel for adesired (or alternatively, predetermined) time interval. Referring toFIGS. 3 and 4, the reserved time interval may span from a time ofbroadcasting a reserve signal (e.g., a CTS-to-self signal) to an end ofthe DTI (e.g., acknowledgement ACK). According to at least one exampleembodiment, step S410 may include refusing uplink transmission requeststhat would overlap the DTI from user terminals associated with theparticipating APs, thereby reducing (or alternatively, preventing) theDTI from being utilized by each of the participating APs' associateduser terminals. For example, a participating AP may refuse uplinktransmissions of associated user terminals when the AP receives a RTSsignal or a header of an uplink packet that will overlap with the DTI.If there is third party traffic on the channel, step S410 may includereducing (or alternatively, excluding) third party transmissions overthe channel. The reservation process is described in more detail belowwith reference to FIG. 5.

Still referring to FIG. 4, in step S420, participating APssimultaneously initiate transmission of the plurality of data packetsduring the reserved time interval. For example, each participating APtransmits a RTS signal at a beginning of a same DTI. According to atleast one example embodiment, this may be accomplished by removingrandom back-off within the MAC protocol of each participating AP. Asshown in FIG. 4, the DTI for each participating AP ends at a same time.Thus, acknowledgments ACKs are received without interference becauseeach AP sets its packet length to be a same length as packets from otherparticipating APs in step S400. Thus, the participating APs uplinktransmission may also be synchronized. In this way, participating APsmay be said to have synchronized transmission intervals.

FIG. 5 illustrates a flow diagram of a method for reserving a channel ina Wi-Fi network according to an example embodiment.

Referring to FIG. 3 and step S500 in FIG. 5, each participating AP setsa variable length look-ahead window based on the packet statistics ofthird party traffic. According to at least one example embodiment, thelook-ahead window contains a time when the channel is available fortransmitting data packets to or from the participating APs. That is, thelook-ahead window may contain a time when the channel is free from thirdparty transmissions. According to at least one example embodiment, thelength of the look-ahead window is set such that, with high probability,participating APs will be able to seize a channel at the start of theDTI.

According to the example reservation method of FIG. 5, eachparticipating AP may perform two seizing operations on a channel.

Referring to FIG. 5, each participating AP waits for the channel to befree from third party traffic for a period of a priority interframespace (PIFS). After the channel is free for the PIFS, each participatingAP may perform a first seizing of the channel to hold the channel instep S510.

According to at least one example embodiment, the first seizing in stepS510 may include refusing uplink transmission requests that wouldoverlap the DTI from user terminals associated with the participatingAPs, thereby reducing (or alternatively, preventing) the DTI from beingutilized by each of the participating APs' associated user terminals.For example, a participating AP may refuse uplink transmissions ofassociated user terminals when the AP receives a RTS signal or a headerof an uplink packet that will overlap with the DTI. If there is thirdparty traffic on the channel, the first seizing in step S510 may includereducing (or alternatively, preventing) third party transmissions overthe channel.

If there is not a possibility for third party traffic on the channel,each participating AP may accomplish the first seizing by broadcasting areserve signal (e.g., a CTS-to-self signal) having a transmissionduration that lasts until the start of the DTI. Here, the reserve signalholds the channel until the participating APs simultaneously initiatetransmission (i.e., until the second seizing). That is, the reservesignal informs user terminals associated with the participating APs tostop sending request to send (RTS) signals. As such, it may be said thatthe participating Aps are holding the channel by refusing uplinktransmissions from the user terminals. If there is a possibility ofthird party traffic on the channel, then the reserve signal may hold thechannel until the end of the DTI. Consequently, third party APs updatetheir network allocation vector (NAV) to ‘busy,’ thereby preventingthird party AP transmissions over the channel during the look-aheadwindow and the DTI.

In step S520, each participating AP performs a simultaneous secondseizing to simultaneously initiate transmission of data by each of theparticipating APs. For example, the participating APs perform the secondseizing at the start of the DTI. As shown in FIG. 3, each participatingAP performs the simultaneous second seizing by broadcasting a RTS signalto seize the channel. Referring to FIGS. 3 and 5, the channel may bereserved from the first seizure to an end of the DTI.

FIG. 5 describes a method of reserving a channel where there is thirdparty traffic on the channel. However, it should be understood thatsteps S510 and S520 would be sufficient for reserving a channel if thereis no third party traffic present. Further, it should be understood thatthe method of FIG. 5 may be implemented as step S410 in FIG. 4.

Synchronization of transmission intervals according to at least oneexample embodiment described above may reduce (or alternatively,prevent) inter-access point interference, reduce (or alternatively,prevent) packet loss, and preserve desired data rates in acommunications network, particularly in a high density communicationsnetwork where multiple access points overlap in coverage. Further,implementation of the above described example embodiments may berelatively simple and cost-effective.

Variations of the example embodiments are not to be regarded as adeparture from the spirit and scope of the example embodiments. All suchvariations as would be apparent to one skilled in the art are intendedto be included within the scope of this disclosure.

What is claimed is:
 1. An access point configured to: generate a datapacket such that the data packet has a same packet length as a datapacket from at least one other access point, predict, if there is thirdparty traffic on a channel, a time when the channel is expected to beavailable for transmitting the data packet based on packet statistics ofthe third party traffic, set a look-ahead window during the predictedtime for the channel, reserve, while within the look-ahead window, thechannel for a time interval, and initiate transmission of the datapacket over the reserved channel at a same time as transmission of thedata packet from the at least one other access point.
 2. The accesspoint of claim 1, wherein the access point is configured to exclude thethird party traffic on the channel during the reserved time interval. 3.The access point of claim 1, wherein the access point is configured torefuse uplink transmission requests for the channel from a user terminalassociated with the access point during the reserved time interval. 4.An access point configured to: predict, if there is third party trafficon a channel, a time when the channel is expected to be available fortransmitting the data packet based on packet statistics of the thirdparty traffic, set a look-ahead window during the predicted time for thechannel, first seize, while within the look-ahead window, the channel tohold the channel, and second seize the channel to initiate datatransmission over the channel, the data transmission for the accesspoint being initiated at a same time as initiation of data transmissionfor at least one other access point over the channel.
 5. The accesspoint of claim 4, wherein the access point is configured to hold thechannel by refusing uplink transmission requests for the channel from auser terminal associated with the access point.
 6. The access point ofclaim 4, wherein the access point is configured to exclude a third partyaccess point from transmitting over the channel during the look-aheadwindow and the data transmission.
 7. A method of synchronizing datatransmission, the method comprising: generating a plurality of datapackets, each data packet being associated with a different access pointin a plurality of access points; predicting, if there is third partytraffic on a channel, a time when the channel is expected to beavailable for transmitting the data packet based on packet statistics ofthe third party traffic, setting a look-ahead window during thepredicted time for the channel; reserving, during the look-ahead window,the channel for a time interval; and simultaneously initiatingtransmission of the plurality of data packets over the channel duringthe reserved time interval.
 8. The method of claim 7, wherein thegenerating includes inserting dummy data into at least one data packetsuch that each data packet in the plurality of data packets has a samepacket length.
 9. The method of claim 7, wherein the simultaneouslyinitiating transmission includes removing random back-off for theplurality of access points.
 10. The method of claim 7, wherein thereserving includes broadcasting a reserve signal to refuse uplinktransmission requests from user terminals associated with the pluralityof access points during the reserved time interval.
 11. The method ofclaim 9, wherein the reserving includes broadcasting a reserve signalduring the look-ahead window by the plurality of access points.
 12. Themethod of claim 11, wherein the broadcasting the reserve signal holdsthe channel until the plurality of access points simultaneously initiatetransmission of the plurality of data packets.
 13. The method of claim7, wherein the reserving includes preventing third party access pointtransmissions over the channel during the reserved time interval.
 14. Amethod of reserving a channel, comprising: predicting, if there is thirdparty traffic on a channel, a time when the channel is expected to beavailable for transmitting the data packet based on packet statistics ofthe third party traffic, setting a look-ahead window during thepredicted time for the channel; first seizing, by a plurality of accesspoints during the look-ahead window, to hold the channel; and secondseizing, by the plurality of access points, the channel tosimultaneously initiate data transmission to or from the plurality ofaccess points.
 15. The method of claim 14, wherein the first seizingincludes refusing uplink transmission requests for the channel from userterminals associated with the plurality of access points.
 16. The methodof claim 14, wherein the first seizing includes preventing a third partyaccess point from transmitting over the channel during the look-aheadwindow and the data transmission.
 17. The method of claim 14, furthercomprising: generating data packets for each of the plurality of accesspoints such that each data packet has a same packet length.